With the rapid technological development in recent years, semiconductor technologies can be applied in more different technical fields, such as in logic computation (e.g. CPU), data storage (e.g. DRAM), and light emitting diode (LED). However, the increasing performances of the semiconductor devices are accompanied by more heat emissions thereof. Therefore, the heat transfer technology is becoming more and more important.
For example, in present time, the luminous efficiency and the brightness of the light emitting diode is accepted by the public, so that the light emitting diode is used widely for example in backlight assembly, car lamp, and street light, etc. However, with the increasing brightness, the larger amount of heat emission from the light emitting diode has become a troublesome issue in the industry. If the heat emission cannot be removed efficiently, the brightness of the light emitting diode will be decreased and the service life will become shorter.
Nowadays, the types of submounts used for packaging the LED device according to respective types of substrates can be divided into four categories: a print circuit board (PCB) substrate, a metal core print circuit board (MCPCB) substrate, a ceramic substrate, and a silicon substrate. In comparing these four types of submounts, the cost of the print circuit board substrate is the lowest, but its heat transfer efficiency is relatively poor. Furthermore, due to the corresponding technical limitations and cost burden, an insulating film residing on the silicon substrate is often relatively thin, so that dielectric breakdown can easily occur. The ceramic substrate is usually in the form of an Al2O3 substrate in the market, but the heat transfer efficiency of the Al2O3 substrate is poor. An AlN substrate, which is one type of ceramic substrate, has higher heat transfer efficiency, but its cost is higher.
Although the MCPCB substrate has higher heat transfer efficiency than the PCB substrate, the improvement of the heat transfer efficiency is still limited by a dielectric layer between a metal layer and a LED die.
Please refer to FIG. 1. FIG. 1 shows a front view of a traditional LED device assembly 100. The conventional LED device assembly 100 is disposed on a circuit board 10. The LED device assembly 100 includes a light emitting diode 110 and a conventional LED package 102. The LED package 102 includes a substrate 120, a reflector 130, and an insulator 140. The substrate 120 is a MCPCB substrate. The light emitting diode 110 and the reflector 130 are both disposed on the substrate 120. The reflector 130 defines a cup-shaped cavity 132. The light emitting diode 110 is disposed in the cavity 132. The sidewall of the cavity 132 has a relatively smooth reflective surface and is able to reflect the light emitting from the light emitting diode 110, so that the directivity of the light is improved. However, the reflector 130 and the substrate 120 are of two different elements, so that after an extended usage period, the reflector 130 may be dislocated or separated from the substrate 120.
In addition, a wire 112 and a wire 114 are connected with the light emitting diode 110. The wire 112 is connected to a positive conductive area 121 of the substrate 120, and the wire 114 is connected to a negative conductive area 122 of the substrate 120. The light emitting diode 110 is disposed in a die-mounting area 123 of the substrate 120. The positive conductive area 121, the negative conductive area 122, and the die-mounting area 123 are separated from each other by the insulators 140. The insulator 140 is formed in the holes of the substrate 120 by the injection of glue. Therefore, the holes should have a diameter larger than a predetermined diameter for allowing the glue injection to be performed in a smooth manner. However, this increases the width of the substrate 120, the distance between the positive conductive area 121 and the light emitting diode 120, and the distance between the negative conductive area 122 and the light emitting diode 120, thus the length of the wire 112 and the wire 114 have also to be increased. Furthermore, the LED device assembly 100 is electrically connected with the circuit board 10 by using a wire bonding method, so that the occupied area of the LED device assembly 100 on the circuit board 10 is increased.
Hence, there is a need in the art for providing a submount used for packaging the LED device or other semiconductor device, thereby having higher heat transfer efficiency, a longer service life, and a smaller occupied area.